Conventionally, hydraulic actuators have been the main choice for use for positioning aerodynamic control surfaces of aircraft. Another type of actuator for positioning control surfaces of an aircraft is an electromechanical actuator.
Failure protection systems for flight control systems that include actuator control systems, where the actuators are hydraulic actuators, are well known. Such systems incorporate redundancy, and use, for example, a loop closure function, a command monitor function, and a servo monitoring function, arranged in conventional configurations, and located in conventional positions within an overall flight control system. However, such conventional failure protection systems are not fully suitable for flight control systems where the actuators are electromechanical actuators. This lack of full suitability is exacerbated in the case of actuators for positioning control surfaces of an unmanned air vehicle (UAV).
Lack of full suitability derives, at least in part, from differences between how hydraulic actuators function compared to how electromechanical actuators function. For example, electromechanical actuators are more prone to jam in safety-critical positions.